Variable resistance device



April 1968 R. E. MISHLER ET AL 3,378,802

VARIABLE RES ISTANCE DEVI CE Filed June 25, 1965 2 Sheets-Sheet l 23 I5 22 7 WM 6 I 1 1 11 2/ 8 I'M- 1 g:

INVENTORS RALPH E. MISHLER LESLIE If PEART 4 DONALD o. PETTIT April? 6, 1963 R. E. MISHLER ET Al. 3,378,802

VARIABLE RESISTANCE DEVICE Filed June 25, 1965 2 Sheets-Sheet 2 FIG. 5 INVENTORS RALPH E. MISHLER LESLIE T. PEAR DON LD D. PET

ATTORNEY United States Patent Ofiice 3,378,802 Patented Apr. 16, 1968 3,378,8tl2 VARIABLE RESISTANEE DEVICE Ralph Ephraim Mishler, Diamond Bar, Leslie Thomas Peart, Santa Ana, and Donald Dalton Pettit, Thousand Oaks, Califi, assignors to Beckman Instruments, Inc, a corporation of California Filed June 25, 1965, Ser. No. 467,042 2 Claims. (Cl. 338-474) ABSTRACT OF THE DISCLOSURE A variable resistance device including a housing defining a recess in which there i mounted for rotational motion a nonconductive rotor having one edge beveled around its outer periphery. The rotor is supported by spacer means above a nonconductive base member carrying an arcuate shaped resistance element with the wiper of the rotor extending into contact therewith. In order to rotate the rotor there is provided an adjustment screw mounted through a side wall of the housing and including a beveled drive head engaged against the beveled surface of the rotor so that rotation of the adjustment screw and its drive head cause the rotor and its electrical contact wiper to rotate within the recess.

The present invention relates to variable resistance devices and is particularly adapted to such devices commonly referred to as trimmer potentiometers.

Variable resistance devices employ a resistance element and a movable contact adapted to traverse the surface of the resistance element in order to vary the voltage drop occurring across a portion of the resistance element. A potentiometer usually includes a resistance element and a pair of terminals connected to opposite extremities thereof with a movable contact which traverses the surface of the element to vary the voltage drop between the respective terminal connections of the resistance element and the movable contact. Potentiometers of the trimmer type function mainly as auxiliary voltage adjusting devices and normally require infrequent adjustment. In most trimmer potentiometers, the mechanical linkage for adjusting the position of the movable contact or wiper is actuated by a screwdriver.

The trend toward miniaturization and weight reduction has created an increased demand for small electrical components which may be utilized in conjunction with such applications as printed circuitry. As the weight of variable resistance devices is decreased, it is advantageous from a manufacturing and cost standpoint to redesign the components and simplify the construction in order to obtain a reasonable degree of accuracy and stability. As the size of such devices is reduced, the design of the mechanism for positioning the adjustable wiper contact becomes exceedingly critical if accuracy and reliability are to be obtained under a reasonable cost basis.

It is an object of the present invention to provide a simplified variable resistance device having an extremely accurate and reliable mechanism for positioning the movable electrical contact.

It is another object of this invention to provide a miniature variable resistance device having a plurality of pin terminals extending from one side thereof and a simple adapter arrangement for converting the device so that the terminals extend from another side the eof.

Further objects and advantages of the present invention will become apparent as the description proceeds, and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

In accordance with a preferred embodiment of the presout invention there is provided a variable resistance device comprising a housing defining a recess in which there is mounted for rotational motion, a circular non-conductive rotor having one edge beveled around the outer periphery thereof. A non-conductive base member is mounted with: in the recess adjacent the rotor and is spaced therefrom by a spacer means which maintains a fixed distance between the rotor and the surface of the base member. Disposed on the surface of the base member is an arcuate shaped electrical resistance element, the surface of which is contacted by a conductive wiper carried by and rotatable with the rotor. In order to rotate the rotor member there is provided an adjustment screw mounted through a sidewall of the housing and retained therein. The adjustment screw includes a bevel drive head tightly engaged against the beveled surface of the rotor so that rotation of the adjustment screw and its drive head causes the rotor and its electrical contact wiper to rotate within the recess. Means including a plurality of pin terminals extend through the base member and make electrical contact with the resistance element and the conductive Wiper carried by the rotor. In order to convert the device so that the pins protrude from another side thereof there is provided a slotted cover having the outline shape of the device and adapted to be attached to the base member and to receive, in individual slots communicating with one edge of the cover, the terminal pins bent at at their exit point from the base member.

For a better understanding of the invention reference may be had to the accompanying drawings in which:

FIGURE 1 is a side elevation view taken in cross section incorporating a preferred embodiment of the invention;

FIGURE 2 is a view of the bottom surface of the rotor and the conductive wiper carried on the rotor;

FIGURE 3 is a plan view of the base member and the electrical resistance element deposited thereon along with a slip ring;

FIGURE 4 is a bottom view of a variable resistance device illustrating its square shape and the arrangement of the pin terminals extending therefrom;

FIGURE 5 is a side elevation view of the variable resistance device taken partially in cross section to illustrate the side pin conversion adapter;

FIGURE 6 is a plan view of the side pin conversion adapter taken substantially along line 6-6 of FIG. 5.

Referring now to FIGURES 1 and 4 of the drawing,

there is shown a trimmer potentiometer 2 in accordance with a preferred embodiment of the invention. The trimmer potentiometer includes a housing 3 having a generally square top and bottom elevation and a substantially rectangular side elevation. The housing includes a centrally located recess 4 formed therein. Different materials may be used to form the housing 3; both die-cast aluminum and molded diallyl phthalate resin have been found to be particularly adapted for this purpose.

One corner of the casing is removed or beveled as at 6 and the sidewall of the casing 3 is provided with an opening 7 adapted to receive an adjustment screw 8 having a slotted head 9 which protrudes from the housing at the corner thereof. As may be seen in FIGURE 1, the adjustment screw extends through the opening 7 and is retained in the sidewall of the housing by a horseshoeshaped retainer clip 10 adapted to fit into a slot formed between the main body of the screw and the bevel gearshaped drive head 11 thereof. The outer surface of the beveled corner of the casing adjacent the opening 7 is counter-bored to form a recess 12 adapted to accept an O ring 13 of resilient sealing material, which seals the opening 7 and serves to retain the adjustment screw 8 securely in position within its opening.

Mounted for rotation within the recess 4 is a rotor 14, which may be fabricated of a non-conducting material such as a molded epoxy resin. The rotor 14 cmprises, in general, an upper cylindrical portion or boss 15 and a larger, concentric lower cylindrical portion 16. At their junction, the cylindrical portions 15 and 16 define a horizontal surface or shoulder 17 the outer extremity of which is beveled at an angle substantially the same as that of the beveled gearhead 11 of the adjustment screw 8. The lower surface 18 of the rotor is substantially planar and the outer edges of this surface of the rotor ride on a spacer 19 disposed between the rotor and a base member or substrate 21 enclosing the opening to the recess 4. The cylindrical boss 15 of the rotor extends into a bearing 22 formed by a cylindrical protrusion 23 extending from the central end wall of the housing 3. Bearing 22 supports the rotor within the recess 4 for rotation around an axis generally coaxially disposed with respect to recess 4.

The base member 21 is formed of a non-conductive ceramic material, such as steatite or an alumina and is positioned within the opening to the recess 4. The base member abuts against the spacer 19 which is, in turn, firmly held within the housing 3 by shoulders 26 formed in the sidewalls thereof. The substrate or base member 21 supports a resistance element 27 and a collector element 28 (best seen in FIGURE 3). The resistance element 27 is in the form of a thin arcuate strip and may be formed of a resistance material of the type commonly referred to as cermet material. Cermet resistance elements and materials may be constructed in accordance with the teachings of US. Patent No. 2,950,995 of Thomas M. Place, Sr., et al. entitled Electrical Resistance Material and US. Patent No. 3,149,002, of Thomas M. Place, Sr., et al., entitled Method of Making Electrical Resistance Element both of which are assigned to Beckman Instruments, Inc., assignee of the present invention. Other type resistance elements, such as conductive plastic and deposited metallic films, may be employed for the variable resistance device.

The collector 28 may typically comprise a thin layer or sheet of deposited platinum or silver material or the like. Means, including terminal pins or members 29 extending through the base member 21, are provided to connect the resistance element 27 and the collector 28 to external electrical circuitry in which the potentiometer or variable resistance device is to be used.

As may best be seen in FIG. 2 a movable contact element 31 is carried on the rotor 16 and includes a conductive wiper represented by the fingers 32. The conductive wiper extends between the surface of the rotor and the surface of the base member and traverses the resistance element 27 during rotation of the rotor. The contact element 31 is staked to the planar surface 18 of the rotor 16 in any manner well known to the art. For example, the surface 18 may be provided with a plurality of bosses 33 which extend through openings formed in the contact member 31 which bosses are heated and pressed to retain the contact member thereon. Or alternatively, the contact member can be cemented or attached by means of small screws to the surface of the rotor. A centrally disposed contact finger 34 forms a part of the contact element 31 and extends into contact with the collector 28 thereby to conduct electrical current to and from the contact member 31 and its associated wiper 32. For better performance, the contact element 34 contains a dimple 36 stamped in the end of the collector finger 34 which furnishes a low friction contact point engaging collector 28.

As stated before, the drive head portion of the adjustment screw is in the form of a bevel gear. The drive head is disposed at the beveled surface of the rotor 16, which is preferably fabricated from a material such as molded molybdenum disulfide nylon. The design and tolerances are such that there is always interference between the teeth 11a of the gearhead and the beveled surface 17a of the rotor. As will be seen in FIGURE 1, the rotor is positioned between the spacer 19 and the gearhead 11 and the interference fit causes the teeth 11a of the gearhead to bite into the beveled surface of the rotor. After the beveled gearhead 11 actuates the rotor 16 through one full revolution, the once smooth beveled surface of the rotor has a mating set of teeth formed thereon. By forming their own teeth, the gears mate perfectly and provide a smooth mechanical drive with nomismatch or backlash. This smooth drive tends to eleminate contact jitter during adjustment and therefore reduces electrical noise. Furthermore, the excellent mating of the gears contributes to the stability of the device, despite vibrations and other influences once a specific setting has been made.

Spacer 19 serves several purposes. It is preferably formed of polytetrafluoroethylene and surrounds the resistance element 27 to provide an insultation medium between the arcuate resistance element and the housing 3, which may be formed of a metallic material. This tends to prevent electrical breakdown between the housing and the resistance element. The spacer also helps position and hold the rotor 16 in place. The surface of the spacer 26 is smooth and serves as a bearing surface for the rotor 16 so that a certain degree of pressure may be exerted in the downward direction by the gearhead 11 which actuates the rotor around its rotational axis.

In the embodiment of the invention shown in FIG- URES 14 the termination pins 29 are spaced so that they match the standard grid of a printed circuit board. The upper end of these terminal pins, which extend into the substrate 21, may be provided with a plurality of serrations so that the pins are securely retained within the substrate. In practice it is desirable to position the pins 29 into holes formed in the green or unfired substrate in the manner described in the copending patent application of Karl Szobonya, Ser. No. 416,074, entitled Terminal Structure also assigned to the assignee of the present invention. Shrinkage of the refractory base memher during the firing or curing operation causes the refractory material to completely surround the void or spaces which exist around the terminal ends 29 and to securely retain them within the base member 21 after the unit has been fired.

While the embodiment disclosed in FIGURES 14 may easily be connected into a standard grid of a printed circuit 'board, it may be desirable to position the terminal pins so that they protrude from another side of the resistance device in order to make it possible to permit access to the adjustment screw from another direction. One preferred arrangement for converting the pin position of the potentiometer device is illustrated in FIG- URES 5 and 6. FIGURE 5 shows the potentiometer or variable resistance device having the pins 29 extending out the base 21 thereof. Positioned over the base member and cemented to the bottom of the housing and base is a conversion cover 36. As may be seen in FIG- URE 6, the conversion cover 36 is provided with a plurality of slots '37 all extending from a common edge 38 of the cover to positions designed to receive the terminal pins arranged in the standard grid pattern. Slots 37 receive the terminal pins 29 which are bent over at as they emerge from the substrate 21 and formed in the shape of the slot. A coating of epoxy or other cement material may be applied to the surfaces of the conversion cover 36 in order to retain it securely against the bottom of the potentiometer or variable resistance device. Once attached to the device the terminal pins 29 are completely insulated one from the other and extend out the common edge of the device for attachment into a suitable electrical circuit or to be extended into suitable holes formed in a circuit board. :In such a position the device is disposed on its common side 39 and 38 so that one may have suitable access to the head 9 of the adjustment screw 8.

While in accordance with the patent statutes there has been described what at present is considered to be the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention and it is, therefore, the aim of the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A variable resistance device comprising:

a substantially square housing having sidewalls and an end wall defining a recess, said housing having one corner relieved to provide a fiat surface disposed at substantially equal angles with respective adjacent sidewalls of said housing;

a bearing member extending from said end wall into said recess;

a circular shaped non-conductive rotor disposed within said recess and having a cylindrically shaped boss extending into said bearing member of said end Wall so that said rotor is rotatable about an axis substantially normal to said end Wall, said rotor having a beveled surface formed around the outer periphery thereof;

a non-conductive base member mounted in said recess,

said non-conductive base member substantially closing said recess and having an inner surface arranged proximate said rotor;

an arcuate shaped electrical resistance element supported on said inner surface of said base member;

spacer means including a non-conductive spacer ring supported on said base member around said outer periphery of said electrical resistance element, said spacer ring abutting said rotor on an outer peripheral surface opposite from said beveled surface and maintaining a fixed distance between said rotor and said inner surface of said base member;

a conductive contact wiper carried by said rotor, said Wiper extending through said space between said rotor and said surface of said base member and being in electrical contact with said arcuate shaped resistance element;

an adjustment screw mounted through said relieved portion of said housing, said adjustment screw having a slotted head accessible from the exterior of said housing and a beveled drive head extending into said recess and including a plurality of sharp teeth engaging the beveled surface of said rotor so that rotation of said adjustment screw and said drive head causes said rotor and its associated electrical wiper to rotate within said recess, said outer peripheral portion of said rotor engaged by said beveled head of said drive screw being supported against said drive screw by a portion of said spacer ring abutting said surface of said rotor directly opposite from said beveled head of said drive screw; and

means including a plurality of terminal members extending through said base member for conducting electrical current to said resistance element and said wiper carried by said rotor.

2. A variable resistance device comprising:

a housing defining a recess;

a circular nonconductive rotor mounted in said recess of said housing for rotation therein, said rotor having a beveled surface formed around the outer periphery thereof on one surface of said rotor;

a nonconductive base member mounted in said recess, said base member having an inner surface arranged proximate said rotor;

an arcuate shaped electrical resistance element sup ported on said inner surface of said base member;

a nonconductive spacer ring supported on said base member around said outer periphery of said electrical resistance element, said spacer ring abutting said rotor on an outer peripheral surface opposite from said beveled surface and maintaining a fixed distance between said rotor and said surface of said base member;

a conductive wiper carried by said rotor, said wiper extending through said space between said rotor and said surface of said base member and being in electrical contact with said resistance element;

an adjustment screw mounted through a side wall of said housing, said screw including means for rotation thereof accessible from the exterior of said housing and a beveled drive head engaging the beveled surface of said rotor so that rotation of said adjustment screw and said drive head causes the rotor and its associated electrical wiper to rotate within said recess, said outer peripheral portion of said rotor engaged by said beveled head of said drive screw being supported against said drive screw by a portion of said spacer ring abutting said rotor on said peripheral surface of said rotor directly opposite said beveled head of said drive screw; and

means including terminal members extending through said base member for conducting electrical current to said resistance element and said wiper carried by said rotor.

References Cited UNITED STATES PATENTS 3,150,343 9/1964 Lippman 338--174 3,235,828 2/1966 Baker 338--174 3,237,140 2/1966 Barden et al. 338-164 3,242,450 3/1966 Bourns et al 338174 X 3,242,452 3/1966 Grunwald et al. 338--162 X RICHARD M. WOOD, Primary Examiner.

J. G. SMITH, Assistant Examiner. 

